1. Technical Field
The present invention relates to a MEMS element and an oscillator.
2. Related Art
MEMS (micro electro mechanical systems), which are one of techniques for forming a minute structure, mean a technique for making a micro electro mechanical system on the order of microns, or the product thereof, for example.
For example, U.S. Patent Application Publication No. 2007/0279140 discloses, as a MEMS element, a MEMS vibrator including a first electrode and a second electrode having a beam portion arranged with a gap between the first electrode and the beam portion. The MEMS vibrator disclosed in U.S. Patent Application Publication No. 2007/0279140 is a cantilever-like vibrator in which one end of the beam portion is fixed and the beam portion has a shape whose size in its width direction is larger than in its extension direction. By making the beam portion large in the width direction in this manner, an electrostatic force between the beam portion and the first electrode can be increased without changing a vibration frequency. When such a MEMS vibrator is used for an oscillator, it is desirable to cause the MEMS vibrator to oscillate at a frequency of the first vibration mode in view of an output signal, for example.
On the other hand, the MEMS vibrator has a plurality of vibration modes, and the frequency of each of the vibration modes depends on the shape of the vibrator. When a vibrator is used as an oscillator in general, it is ideal that differences in frequency between a vibration mode to be used and other vibration modes are large. For example, in the case of using the first vibration mode as an oscillator, when a difference between a frequency of the first vibration mode and a frequency (spurious) of the second vibration mode is small as shown in FIG. 14, there is a problem in that the vibrator oscillates in an oscillation condition satisfied by the second vibration mode.
Especially in the case of the MEMS vibrator having the beam portion larger in the width direction than in the extension direction as described above, a difference in frequency between the first vibration mode and the second vibration mode is small. Therefore, oscillation is likely to occur at an unintended frequency.